The use of catheters to insert and position therapeutic devices in the vasculature has become a widely-used form of treatment for various conditions. Such devices are particularly useful in treating areas where traditional procedures are difficult such as in narrow cranial blood vessels. For example, vaso-occlusive devices such as embolic coils or wires are inserted at sites of aneurysm to occlude blood flow. The decreased blood flow reduces the pressure on the aneurysm and reduces the risk of a ruptured aneurysm. The coil also promotes thrombus formation. Embolic coils and wires can assume different shapes to better occlude a blood vessel. The coils can be coated with various materials to improve thrombogenicity. U.S. Pat. No. 6,723,108 describes some of the characteristics of different shapes of embolic coils. This patent and all other patents and references identified herein are hereby incorporated herein by reference.
Typically, procedures using a catheter involve inserting the distal end of the catheter into the vasculature of a patient and guiding it to a predetermined delivery site. A therapeutic device, such as an embolic coil, is attached to the distal end of a pusher element such as a wire that can be used to manipulate the therapeutic device. For example, the wire is used to push the coil through the catheter and out of its distal end into the delivery site. The coil is then released from the pusher element. The small sizes of some blood vessels require that a mechanism which releases the coil from the pusher be simple and not required complicated equipment. In addition, the release must accurately and rapidly place the therapeutic device at the determined site. Problems that have been associated with the release of the coil include the force of the coil exiting the delivery catheter causing the coil to overshoot the desired site or dislodge previously deployed coils.
In response to the above mentioned concerns, numerous devices and release mechanisms have been developed in an attempt to provide a delivery system which provides a rapid release or detachment mechanism to release the device at the correct location. One such device is disclosed in Geremia et al. U.S. Pat. No. 5,108,407, which shows a fiber optic cable including a connector device mounted to the end to the optic fiber. An embolic coil is attached to the connector device by a heat releasable adhesive. Laser light is transmitted through the fiber optic cable to increase the temperature of the connector device, which melts the adhesive and releases the embolic coil. One drawback to using this type of system is the potential risk of melted adhesives contaminating the blood stream.
Yet another embolic coil positioning and delivery system is described in Saadat et al. U.S. Pat. No. 5,989,242, which discloses a catheter having a shape memory alloy connector attached to the distal end of the catheter. The connector includes a socket having a pair of spaced-apart fingers which are responsive to a change in temperature. The fingers are bent towards each other and hold a ball which is connected to an end of an embolic coil. The connector absorbs laser light transmitted through an optical cable and transforms the light into heat energy. The heat energy raises the temperature of the connector and opens the fingers, thereby releasing the embolic coil. This type of ball and socket connection is rigid and causes the catheter to be stiff, making it difficult to guide the catheter through the vasculature of the body.
In keeping with the invention, a need is recognized for a rapid, simple therapeutic device delivery apparatus that is elegant in design, relatively simple to manufacture, flexible and easy to guide through the vasculature of the body and which provides excellent control over the device.